1. Field of the Invention
This invention relates to the field of paper shredders for quickly shredding large amounts of paper in an office environment to meet security requirements for classified, i.e., confidential, secret, top secret and communications security materials. To this end, shredders must shred at least from about 40-100 sheets of letter-size paper at a rate of one second per sheet to shreds of at least as small as 1/32".times.1/2" shreds.
2. Description of the Prior Art
The field of commercial paper shredders is well established. One patent that is illustrative of this field is U.S. Pat. No. 4,034,918, which describes a pair of counterrotating shafts for mounting a series of spaced apart disc-type cutters. These shafts are driven by a reversible drive means having forward and reverse motions which are controlled by a suitable control means for intermittent operation. While oiling attachments for intermittently operated machines, such as presses, have been available as described in U.S. Pat. No. 1,246,886, these oiling attachments have been troublesome or inapplicable to commercial paper shredders.
It has now been found desirable to reduce the downtime and/or maintenance costs and/or to increase the longevity of paper shredders without increasing their cost, decreasing their efficiency or compromising their safety. Indeed, it is desirable to decrease their cost and/or increase their efficiency while maintaining or improving their safety.
One problem in improving the shredders known heretofore has been the nature of their cutting heads and their manufacture. They have been conventionally made by specialty companies from a large number of hard-to-manufacture, heavy-duty, cutting knives of expensive, high-quality, hardened steel. In a typical commercial cutter, 461 special steel, custom-made knives have been required to be made. Moreover, each knife has been as small as 1/35 inch thin.times.3/8 or 7/8 inch. Still further, the knives have been sharpened to provide knife-like edges and/or machined to have spiral grooves for ease in shredding every paper fed into the shredder in a failsafe manner. Additionally, these shredders have been required to quickly produce unreadably small particles that could not reasonably be reassembled into readable form. Thus for example, an ordinary paper shredder has been required to shred a letter-sized 81/2" by 11" paper into at least 10,000 particles in a second. This has required the rapid rotation of these special steel knives at speeds up to 1000 RPM by large heavy duty motors and/or gears. This has caused a tendency for the knives to overheat and/or to dull repeatedly. It is additionally desirable to provide improved cleaning.